An enzyme-immunoassay for the determination of carcinoembryonic antigen (CEA) is described by Maiolini et al., in Clinical Chemistry 26/12, 1718-1722 (1980). According to this assay, pre-treated serum or plasma samples are incubated in a first step for two hours at 45.degree. C. with beads which are sensitized with guinea pig-anti-CEA. After a washing step, the beads are incubated for two hours at 45.degree. C. with a conjugate of goat-anti-CEA and horseradish peroxidase. After removing excess conjugate by washing, the enzyme activity is determined on the solid phase according to known methods. By comparing this value with a standard curve prepared in an analogous manner the content of CEA in the sample is ascertained.
The above noted enzyme-immunoassay method for the determination of antigens, in the present case of CEA, is generally known as the so-called solid phase-sandwich method.
It is a primary object of the present invention to provide a method for carrying out the enzyme-immunoassay without the time-consuming and laborious washing step between the first and the second immunological reactions without loss of sensitivity and in the same time-span.
Furthermore, it has been found that by using the process of the present invention, the two-step method in accordance with Clinical Chemistry (loc.cit.) can also be shortened in time, in that the second incubation can be carried out without loss of sensitivity in half the time, i.e. in one hour.